1. Field of the Invention
The invention relates to stain-resistant polyamide compositions and fibers and articles of manufacture formed therefrom.
2. Description of the Prior Art
Textile and carpet yarns prepared from polyamide fibers are subject to staining by a variety of foods, drinks and many other compositions with which it comes in accidental contact. The uptake of acid dye stains from, for example, soft drinks, is a particularly vexing problem for polyamide fibers due to the availability therein of acid dye sites such as amine end groups and amide linkages. Several methods have been suggested for enhancing the resistance of polyamide fibers to acid dye stains.
One approach is to apply a so-called xe2x80x9cstain blockerxe2x80x9d coating to the surfaces of polyamide fibers to prevent access to the acid dye sites therein by the acid dye staining composition. An example of such a method is illustrated by U.S. Pat. No. 5,145,487 which discloses coating the fibers with sulfonated aromatic condensates (SACs). Similar proposals are suggested in U.S. Pat. Nos. 4,680,212 and 4,780,099.
Another approach is to form the fibers from polyamides prepared by copolymerizing monomers, some of which contain sulfonate moieties. Typical of such systems are those disclosed in U.S. Pat. Nos. 3,542,743; 3,846,507; 3,898,200 and 5,108,684.
U.S. Pat. No. 4,374,641 relates to pigment concentrates made using sulfonated polymers as carrier resins including the highly sulfonated polyamides disclosed in U.S. Pat. No. 3,846,507. U.S. Pat. No. 5,236,645 represents an improvement on the invention claimed in U.S. Pat. No. 4,374,641.
Fibers are generally prepared from polyamides by melt-spinning. Sulfonate containing copolymers generally have higher melt viscosities than non-sulfonate containing copolymers for equivalent relative solution viscosities which limits the extent of polymerization which can be achieved in batch autoclave reaction vessels due to the retardation thereby of the rate of polymerization, as well as its hindrance of effective discharge of the polymerized melt from the reactor. In addition, the presence of sulfonates which have surfactant properties promotes excessive foaming during the melt polymerization process resulting in poor agitation of the reaction mixture and non-uniformity of product.
Yarns having different depths of color require different levels of stain protection. Thus, light shaded colors show the presence of stains more than darker colors. It would be advantageous, therefore, to be able to provide different levels of stain resistance to polyamides depending upon the ultimate yarn color without having to provide a separate polyamide feedstock for optimum formulation of each color yarn.
An additional disadvantage associated with sulfonate containing polyamide copolymers is that they are generally more difficult to dry than sulfonate-free polyamides due to the hygroscopic nature of sulfonate groups.
Polyamides that are topically coated to give stain resistance to the fiber, e.g., with SACs, have the disadvantage that the topical coating is removed during use and maintenance. Gradual removal of the coating will also occur during cleaning with water and detergents. Fibers used for carpet applications may be regularly cleaned with alkaline-based cleaning agents. SAC topical coatings are easily removed using these types of cleaning agents. The topical coating will also be gradually removed during normal wear of the fiber in its chosen application. In addition to their removal during use and maintenance, SACs generally have inferior resistance to light, oxides of nitrogen, and bleach, the latter of which is commonly used for the cleaning of industrial textiles and carpets. Also, the base color of SACs is not colorless and thus may change the shade of the color of the yarn.
It is an object of the present invention to provide a novel and highly advantageous approach for imparting stain resistance to fibers formed from polyamides.
The above and other objects are realized by the present invention, one embodiment of which comprises an acid dye stain-resistant fiber-forming polyamide composition comprising:
a. a fiber-forming polyamide; and
b. a reagent at least a portion of which associates with free acid dye sites in the polyamide, thereby disabling the acid dye sites in fibers formed from the composition from taking up acid dye stains.
Another embodiment of the invention relates to a masterbatch concentrate for addition to a fiber-forming polyamide to form the above-described acid dye stain-resistant fiber-forming polyamide composition, the concentrate comprising a carrier material compatible with the fiber-forming polyamide, preferably a polyamide, combined with an amount of the reagent in excess of that desired in the acid dye stain-resistant fiber-forming polyamide such that addition of the concentrate to the compatible fiber-forming polyamide results in the desired level of stain resistance.
An additional embodiment of the invention concerns stain-resistant fibers formed from the above-described polyamide compositions.
Further embodiments of the invention comprise articles of manufacture prepared with fibers according to the invention such as textiles and carpets.
A final embodiment of the invention relates to a method of forming acid dye stain-resistant fibers comprising forming a polyamide composition according to the present invention into fibers by, for example, melt spinning.
The terms below have the following meanings herein, unless otherwise noted:
xe2x80x9cReagentxe2x80x9d refers to any chemical compound, composition or material which associates (as that term is defined below) with the free acid dye sites in a fiber-forming polyamide to thereby render them unavailable for association with an acid dye, which reagent is incapable itself of associating with or taking up the acid dye.
xe2x80x9cAssociationxe2x80x9d refers to the chemical reaction or bonding between the reagent and the free acid dye sites in the polyamide which results in prevention of xe2x80x9ctaking upxe2x80x9d of the acid dye by the polyamide, i.e., staining. The association may take the form of a chemical reaction or an acid-salt formulation. Additional types of association include hydrogen bonding, dipole-dipole interaction, Van der Waals forces and coordination complexing.
xe2x80x9cAcid dye stainxe2x80x9d refers to any material or composition which functions as an acid dyestuff by reacting with the free dye sites in polyamides to substantially permanently color or stain the latter.
The term xe2x80x9cacid dye sitesxe2x80x9d refers to those basic sites in polyamides (e.g., amine end groups, amide linkages, etc.) which react or associate with acid dyes, thereby resulting in a stain bonded thereto.
xe2x80x9cDisablingxe2x80x9d the acid dye sites from taking up acid dye stains refers to the effect of the association between the reagent and the acid dye sites which renders the latter less capable of associating with acid dyes such as, for example, those in soft drinks, tomato-based products, etc., which result in staining.
The present invention is predicated on the discovery that optimum levels of resistance to acid dye stain may be imparted to polyamide fibers by compounding certain reagents with fiber-forming polyamide compositions subsequent to polymerization of the polyamide and prior to the formation of the fibers. The invention thereby enables avoidance of the above-enumerated disadvantages associated with coating the polyamide fibers with stain resistant SACs and with formation of the polyamides by copolymerizing sulfonate containing monomers.
The selection of a suitable non-acid dyeable reagent having at least one functional group capable of associating with the acid dye sites available in fiber-forming polyamides, thereby rendering those dye sites unavailable for association with acid dye stains, enables the formation of stain-resistant fibers having predetermined and optimum levels of stain resistance not obtainable by the methods and systems of the prior art.
Suitable such reagents include those having at least one functional moiety which preferentially associates with the active acid dye sites in the fiber-forming polyamide and, additionally, contains at least one sulfonyl group. The reagent, of course, should be otherwise substantially inert with respect to the fiber-forming properties of the polyamide.
Exemplary of such reagents are those having the formula: 
wherein:
Q and Z are moieties which associate with the acid dye sites in the polyamide;
a is an integer from 0 to 2;
b is an integer from 1 to 4; and
R is aliphatic, aromatic or alicyclic.
The reagent is selected so as to preferentially associate with the amine end group and/or amide linkage acid dye sites in the polyamide. Preferably, a substantially colorless reagent is selected unless, of course, the reagent is expected to contribute a desired color to the fibers prepared from the polyamide.
The associative functional moieties, Q and Z, may comprise any chemistry that will associate with amine or amide linkages, providing that the functionality does not promote increased stain uptake or otherwise deleteriously impact on the ultimate polyamide composition or articles manufactured therefrom. Thus, Q and Z are preferably combined to form carboxylic anhydride groups or are, individually, carboxylic acid groups or alkali metal, alkaline earth metal or transition metal salts thereof; isocyanate groups; epoxy groups; ester groups and xcex1,xcex2diketone groups. Thio functionalities are generally not employed due to their promotion of yellowing in fibers prepared from polyamide compositions containing them when subjected to light, heat, oxides of nitrogen, etc.
The backbone of the reagent or R may be any suitable aliphatic, aromatic, alicyclic or heterocyclic structure such as phenyl, naphthyl, alkyl (straight or branched chain), cycloalkyl including substituted cycloalkyls, aralkyl, alkenyl and cycloalkenyl.
Exemplary of such reagents are 5-sulfoisophthalic acid, 3-sulfobenzoic acid, 4-(acetoacetamido)benzene sulfonic acid, 4-isocyanatobenzene sulfonic acid, 4-(2,3-epoxypropyl)benzene sulfonic acid, dimethyl-5-sulfoisophthalate, 3,5-di-(2,3-epoxypropyl)benzene sulfonic acid, 3,5-di-isocyanatobenzene sulfonic acid, 3,5-di-(acetoacetamido)benzene sulfonic acid, the sodium and lithium salts of all of the above, and sodium or lithium salt of sulfophthalic anhydride.
The invention is applicable to provide acid dye stain resistance in any fiber-forming polyamide such as nylon-6, nylon-66, MXD-6, nylon-11, nylon-12, nylon-69, the amorphous polyamides such as the copolymer of terephthalic acid and trimethylhexamethylene diamine. Other suitable amorphous polyamides include nylon-6,I (a copolymer of hexamethylene diamine and isophthalic acid), terpolymer of lauryllactam, isophthalic acid and bis(4-amino-3-methylcyclohexyl)methane and polynorbornamide.
The composition may include any of the conventional adjuvants for enhancing the formation of fibers from the polyamide composition such as anti-oxidants, stabilizers, colorants, processing aids, anti-static agents, flame retardants, fillers, nucleating agents, anti-microbials, melt viscosity enhancers or mixtures thereof. Catalysts and/or reducing agents can be added to enhance the association of the reagent with the fiber-forming polyamide. Examples of suitable catalysts/reducing agents include salts of hypophosphites such as sodium hypophosphite, ammonium hypophosphite and manganese hypophosphite, or other phosphorus-containing organic compounds such as phenylphosphinic acid, polyphosphoric acids and triphenyl phosphite.
The compositions are prepared by combining the reagent(s), polyamide(s) and, optionally, adjuvant(s) under conditions which ensure association between the functional moieties of the reagent and the free acid dye sites in the polyamide(s). Preferably, the polyamide(s) and reagent(s) are combined by melt blending at temperatures above the melting point of the polyamide(s), but below the decomposition temperature of the reagent(s). The reagent(s) and polyamide(s) may be combined in a pre-fiber spinning compounding operation or directly in the fiber melt spinning stage. Product fibers made according to the invention show durable stain-resistant properties equivalent or superior to those produced according to the prior art methods without the consequent disadvantages attendant thereto.
The reagents (and adjuvants, if any) may be combined with the polyamide(s) in any suitable form such as powdered, pelletized, encapsulated, etc. The polyamide(s) may be employed as powder, granules or pellets. The reagent(s) and adjuvant(s) are preferably combined with the polyamide(s) employing a melt extruder and, most preferably, a screw-type extruder. Optimally, a twin-screw extruder of the fully intermeshing type with both screws rotating in the same direction (co-rotating) is employed, although other types of twin-screw extruders may be used such as counter-rotating and/or non-intermeshing types. Single screw extruders may also be successfully employed. The extruder preferably has a barrel length to screw diameter ratio of about 24:1; however, it will be understood that any suitable ratio may be employed depending upon the parameters of the particular compounding process contemplated.
While it is in no way intended to limit the invention by the soundness or accuracy of any theory set forth to explain the nature of the invention, it is postulated that, during the processing step(s), the stain-resistant reagent at least partially associates with, or reacts with, reactive chemical groups or acid dye sites on the polyamide, such as amine end groups or amide linkages. Removal of volatiles from the compounding mixture aids this association and/or reaction with the polyamide. This removal of volatiles is achieved preferably by the presence of one or more vents on the extruder barrel, although venting is not a requirement for the process of the invention. When a single vent is used with an extruder of a length to diameter ratio of 24 to 1, the vent port is suitably located approximately 19 screw diameters down the length of the barrel. The optimum position of the vent port is determined by the extruder screw profile used. The extraction of volatiles through the vent port is preferably vacuum assisted with a vacuum level of greater than 10 in. Hg and preferably greater than 20 in. Hg. The rate of devolatilization can be assisted through substantially dry nitrogen gas injection through an inlet port located either upstream or downstream of the vent port. Under this situation, a lower vacuum level may be acceptable. Additional ways of promoting the association and/or reaction with the polyamide are through controlled drying of the feedstocks, addition of water-scavenging additives, or a combination of these methods.
The stain-resistant additives and the polyamide resin are preferably fed to the extruder in a pre-dried form with a controlled moisture level. The moisture levels of both the additive and the resin are less than 3,000 ppm and are preferably less than 500 ppm. When drying both of these materials, an inert gas drying atmosphere is preferred. The reagent and the resin may be either fed to the extruder as a blend of the two materials using a single feed hopper or by using separate feed hoppers of a suitable type such as gravimetric or volumetric feeders. Additives to enhance the relative viscosity (RV) of the concentrate can also be added at this stage. When a blend of the materials is used, a double cone tumbler blender is preferred for preparation of the blend, although other types of blenders may be used.
The extruder temperature profiles used and the desired melt temperature during the mixing process will depend, as noted above, principally on the polyamide type and grade chosen. For example, when PA6 is utilized, the melt temperature preferred is between 240xc2x0 C. and 260xc2x0 C. and for PA66 the preferred melt temperature range is between 265xc2x0 C. and 285xc2x0 C. The optimum melt temperatures for these two resin types will depend on the grade employed.
A preferred embodiment of the invention relates to the preparation of a masterbatch concentrate of polyamide and reagent which can be blended with a suitable fiber-forming polyamide prior to or at the melt-spinning stage to achieve the desired level of stain resistance.
Only a small proportion of the reagent is reacted with the polyamide of the concentrate. The bulk of the reagent is dispersed/associated with the resin. It is desired that a proportion of the unreacted reagent in the concentrate becomes reacted/associated with the fiber-forming polyamide. Nylon copolymers are conventionally produced via condensation polymerization where water (or other small volatile molecule, depending on the chemistry) is generated as a by-product. In order to drive this equilibrium reaction forward, it is necessary to remove this water by-product from the system below the equilibrium water concentration. If this is achieved in the fiber spinning line, then association/reaction of the unreacted reagent in the concentrate with the fiber-forming polyamide will occur. In a conventional fiber spinning line, a non-vented extruder barrel is typically used, although vented extruders may be used. The water concentration can be reduced to below the equilibrium value by any of the methods discussed hereinabove.
The masterbatch concentrate may be prepared according to the methods described above employing levels of reagent up to about 50% by weight based on the weight of the polyamide.
Any suitable carrier compatible with the fiber-forming polyamide may be employed to prepare the masterbatch concentrate. Although it is preferred to utilize a polyamide carrier, it will be understood that any suitable polymer, polymer blend or other carrier material which is compatible with the fiber-forming polyamide may be employed. Suitable other carriers include polyesters and modified polyolefins. The polyamide used to prepare the masterbatch concentrate may be the same or different in chemical composition from that of the fiber-forming polyamide with which the concentrate is combined to produce the ultimate composition from which fibers according to the invention are formed.
When a stain-resistant concentrate or masterbatch is produced, the melt emerging from the die of the compounding extruder is stranded through a water batch to solidify the melt, followed by air drying of the strand to remove the bulk of the surface water, and pelletization. The concentrate pellets formed are then dried prior to fiber melt spinning to a moisture level of less than 3,000 ppm and preferably less than 500 ppm. This drying of the concentrate is preferably accomplished in an inert gas atmosphere. The concentrate is then mixed on the fiber melt spinning line with non-stain resistant polyamide resin feedstock, dried to a moisture level of less than 3,000 ppm and preferably less than 500 ppm, in the desired ratio depending on the level of stain resistance required in the fiber product. The fiber melt spinning process of a conventional type is used, familiar to those skilled in the art. Other additives such as colorants and stabilizers may be added during the fiber formation process.
The polyamide resin should have a relative solution viscosity of equal to or greater than 2.4 and preferably equal to or greater than 2.7. The relative viscosity of the resin is determined by first preparing 0.55% w/w solutions of the pre-dried polyamide in concentrated sulfuric acid (analytical grade, 96xc2x10.5%). Solution flow times are determined in a Cannon-Ubbelhode size 2 viscometer suspended in a viscometer water bath controlled at 25xc2x0 C.xc2x10.02xc2x0 C. The flow times of the sulfuric acid are also measured. The relative viscosity is calculated by dividing the flow time of sample solution by the flow time of the solvent. The polyamide resin should also have an amine end group (AEG) level of less than 60 equivalents per 106 g and preferably less than 45 equivalents per 106 g. The AEG level is determined by means of a potentiometric titration. A known weight of sample is dissolved in m-cresol and titrated against 0.1 M perchloric acid in methanol. A blank titration is also carried out on the m-cresol and used to correct the sample titre.
In the following examples, a standard test is used to evaluate the stain resistance of the yarn formed. It involves the use of an acidified solution of FDandC Red 40 dye which is present in the soft drink cherry-flavored Kool-Aid(copyright) commercially sold by Kraft General Foods, Inc.
Typically, 0.1000 gxc2x10.0030 g of FDandC Red 40 dye (CI Food Red 17) is dissolved in 1,000 cm3 of distilled water. The pH of the dye solution is adjusted to between 2.80 and 2.90 by making small additions of citric acid of technical grade or better. The pH adjusted solution is allowed to reach room temperature, i.e., 21xc2x0 C.xc2x11xc2x0 C., prior to use.
1.0000xc2x10.0010 g of yarn is placed in 50 cm3 of the Red 40 solution in a 100 cm3 glass beaker and the yarn is briefly stirred in the solution to ensure that it is fully wetted by the solution. The beaker is allowed to stand for 60 minutes without any further agitation.
The yarn is washed for 120 seconds under free-flowing hot tap water, that is at a temperature of 40-50xc2x0 C. The yarn is then dried by initially blotting with a clean white paper towel to remove the bulk of the surface moisture, followed by allowing it to sit at room temperature for at least 16 hours.
The stain resistance of the yarn is-determined by visual comparison to the AATCC Red 40 Stain Scale, which is available from the American Association of Textile Chemists and Colorists (AATCC), Research Triangle Park, N.C. The scale consists of ten film squares colored with gradually increasing strengths of FDandC Red 40 numbered from 1 to 10, with 1 being the strongest color and 10 being colorless. The unstained yarn is placed underneath the colored portions of the scale and the stained yarn is placed underneath the colorless portion of the scale and viewed under daylight or equivalent illuminant. The light should be incident upon the surfaces at an angle of 45xc2x0xc2x15xc2x0 and the viewing direction should be 90xc2x0xc2x15xc2x0 to the plane of the surfaces. The stained yarn is compared to the unstained yarn placed under the closest numbered colored square of the stain scale so that the best color match is obtained. If the color of the stained yarn falls between two squares on the scale, then half grades are used. The number of this colored square, or squares if the match falls between two squares, is called the Stain Rating.